This invention relates to a multi-break circuit breaker comprising a plurality of vacuum-type circuit interrupters electrically connected in series and, more particularly, relates to means for controlling the voltage distribution between the interrupters.
A common way of controlling the voltage distribution between the interrupters of a multi-break circuit breaker is by connecting capacitors of appropriate size directly across the individual interrupters. This technique is described in detail in U.S. Pat. No. 2,840,670-Leeds, where it is pointed out that one of the problems involved in using this technique is to overcome the effects of capacitance-to-ground between the high voltage parts and ground. As is recognized by Leeds, one approach that can be used to overcome the effects of such capacitance-to-ground is to increase the size of the voltage distributing capacitances across the interrupters, especially across the end interrupters of the circuit breaker.
There are, however, certain disadvantages to this approach. For example, if one of the interrupters should spark-over, causing a discharge of the relatively large capacitor connected thereacross, the resulting relatively large energy transfer will induce unfavorable electrical transients in the system that can force a breakdown of the circuit breaker itself. The chances for such a breakdown are increased if the interrupter that first sparks-over is an end interrupter which has a greater amount of capacitance across it than the other interrupters.
Another disadvantage of connecting large capacitances directly across the interrupters is that spark-over of an interrupter will collapse the voltage across the sparked-over interrupter for an appreciable time, causing the full voltage to appear across the remaining interrupters, which voltage may be distributed in an unfavorable manner that forces a breakdown of these remaining interrupters.
In a vacuum-type circuit breaker, still another problem results from connecting a large capacitor directly across an interrupter. More specifically, the presence of a large capacitor connected directly across a vacuum-type interrupter seems to detract from the capacitance-switching ability of the vacuum interrupter. The reasons for this are not fully understood, but one of them seems to be that the high peak currents resulting from discharge of a large capacitor through a vacuum interrupter upon spark-over materially reduce its dielectric strength. High dielectric strength is needed by the interrupter for good capacitance-switching performance.